Tiny fossils that were once thought to be indications of the first animal life …

An X-ray scan of a fossil embryo, set against the rocks it was isolated from.

Photograph by Swedish Museum of Natural History

The history of the first animal life remains somewhat confused. Ediacaran fossils are clearly multicellular, but lack many of the features shared by all modern animals. In the ensuing period, the Cambrian, all of these organisms are gone, and most of the groups we're familiar with—along with a few unfamiliar ones—are present. The transition between the two is murky.

Spectacular fossils from Doushantuo in China appeared to resolve this issue. The tiny remains date from the Ediacaran, but appeared to share features with animal (more properly, metazoan) embryos, suggesting that metazoans were around for many millions of years, even though we've been unable to identify any fossils of their adult forms. Since their initial announcement, however, this interpretation has been challenged, with some even suggesting that the fossils were little more than clusters of bacteria.

Now, a group has performed X-ray imaging of the internal structure of the fossils and concluded that they most certainly aren't bacteria... but it's not actually clear what they are. The most likely identity, according to the researchers, is a relative of the first metazoans.

First, the new data. The authors have essentially performed a CAT scan of these tiny fossils, except they use energies high enough to fry human tissues. This is sufficient to reveal subtle internal features, including what appears to be a nucleus inside many of the cells, as shown above. The authors argue that this isn't just a matter of similar appearance. The object has a consistent location within the cells, takes up a consistent fraction of the cell's volume, and only appears once per cell, all of which are features of a nucleus.

That clearly eliminates bacteria as a source of these fossils, and would appear to put metazoans back on the table, since these fossils are eukaryotes with multiple cells. But there are still some problems with this interpretation. For example, all the cells appear identical, while metazoans are notable for having multiple specialized cell types. In addition, other fossils from the same deposit appear to lack internal nuclei. Instead, they appear to contain large numbers of individual cells.

The authors interpret this as an indication of a sort of sporulation. A number of organisms reproduce by forming a spore and then divide internally within it, making a large number of identical cells that eventually burst out when the spore germinates and then live independently as single cells. In fact, the authors identify a number of fossils that can be interpreted as in the process of germination. Metazoans, at least existing species of metazoans, don't do this. So, animals remain off the table.

But that doesn't mean these things don't tell us anything about the evolution of metazoans. Metazoans are a subgroup of what are called Holozoans, which is a grab-bag of everything that evolved once we parted ways with the fungi (which went multicellular separately). Some of the holozoans that survive display precisely the mode of reproduction that the authors describe in these fossils, and the clustering of cells in these spores certainly could provide an opportunity for specialized cells to evolve. So, if these fossils don't represent actual metazoans, there's a good chance that the organisms here set the stage for them.

That paints an appealing picture, but there are still a few issues here. For one, there clearly were multicellular organisms in the Ediacaran, and (as far as I'm aware) we don't know what their embryonic stages looked like. Since we're not quite sure of what existing organisms they'd group with, we don't even have a strong idea of what their embryos should look like.

Plus the first metazoans we see in the Cambrian are generally tiny, and heavily biased towards things with skeletons or shells. If they were around earlier, but lacked shells, it's possible we could miss them. And then there's the molecular evidence, which suggests that many of the major groups of organisms that appear in the Cambrian had probably been separated for a significant amount of time in order to evolve their distinct body plans. All of that would suggest that the metazoans probably predate the Cambrian.

So, even if this turns out to be the last word on the Doushantuo fossils, it probably won't be the last word on the origins of animal life.

Well a simple general model is that the complexity of eukaryotic cells evolved over a long time until it reached a threshold. At that point there was a rapid radiation of various multi cellular organisms. One line in this radiation proved dominant and the rest faded away. The transition from single celled eukaryotic organisms to multi celled eukaryotic organisms is pretty minor. Its just some adjustment to the social organization of the cells. The development of tissues is clearly more complicated. But muscle certainly involved no new proteins. Actin is the most fundamental protein of all animal cells. Nerve is not likely to have involved major new mechanisms either. Cells just got specialized around sensory mechanisms that were already used by single celled organisms. Clearly a fair amount of evolution is required to achieve the cell differentiation in the body plan of the prototype bilateral metazoan and for the basic developmental processes that generate that body plan from a single fertilized cell. But, it is hard to tell how much time was required. After all humans arrived in something like five million years and the consequences of human arrival could turn out to be more significant than the appearance of metazoans. If humans learn how to reengineer our being, it probably will be the most significant event since the emergence of life. That event could easily happen this century.

Well a simple general model is that the complexity of eukaryotic cells evolved over a long time until it reached a threshold. At that point there was a rapid radiation of various multi cellular organisms. One line in this radiation proved dominant and the rest faded away. The transition from single celled eukaryotic organisms to multi celled eukaryotic organisms is pretty minor. Its just some adjustment to the social organization of the cells. The development of tissues is clearly more complicated. But muscle certainly involved no new proteins. Actin is the most fundamental protein of all animal cells. Nerve is not likely to have involved major new mechanisms either. Cells just got specialized around sensory mechanisms that were already used by single celled organisms. Clearly a fair amount of evolution is required to achieve the cell differentiation in the body plan of the prototype bilateral metazoan and for the basic developmental processes that generate that body plan from a single fertilized cell. But, it is hard to tell how much time was required. After all humans arrived in something like five million years and the consequences of human arrival could turn out to be more significant than the appearance of metazoans. If humans learn how to reengineer our being, it probably will be the most significant event since the emergence of life. That event could easily happen this century.

Well a simple general model is that the complexity of eukaryotic cells evolved over a long time until it reached a threshold. At that point there was a rapid radiation of various multi cellular organisms. One line in this radiation proved dominant and the rest faded away. The transition from single celled eukaryotic organisms to multi celled eukaryotic organisms is pretty minor. Its just some adjustment to the social organization of the cells. The development of tissues is clearly more complicated. But muscle certainly involved no new proteins. Actin is the most fundamental protein of all animal cells. Nerve is not likely to have involved major new mechanisms either. Cells just got specialized around sensory mechanisms that were already used by single celled organisms. Clearly a fair amount of evolution is required to achieve the cell differentiation in the body plan of the prototype bilateral metazoan and for the basic developmental processes that generate that body plan from a single fertilized cell. But, it is hard to tell how much time was required. After all humans arrived in something like five million years and the consequences of human arrival could turn out to be more significant than the appearance of metazoans. If humans learn how to reengineer our being, it probably will be the most significant event since the emergence of life. That event could easily happen this century.

If humans learn how to reengineer our being, it probably will be the most significant event since the emergence of life. That event could easily happen this century.

If you mean clones, I'm not looking forward to that... First, considering that all new, advanced technologies are usually used first for military purposes, this won't be pretty. Second, the planet is already overcrowded so we don't need more humans, artificial or not.

Creating individual organs for transplants that are matched with the receiver's body. so they won't be rejected and won't require lifetime of medications, seem more possible and useful. But, as much as I enjoy Sci-Fi and armies of clone soldiers in white armor, in reality cloning humans is not needed and it would rise all kinds of moral issues even for non-religious people.

An amazing article, it's stuff like this I love to read. The further back in the evolution of life - the more fascinating it becomes to me. I wonder how old the rock is that these fossils were pulled from, I know they're Ediacaran in age - but a mya figure would help get the idea if it was early, middle, or late. I'm hoping future fossil finds push back the appearance of multicellular life to the start of the Ediacaran, if not into the preceding Cryogenian.

dnjake writes: " Actin is the most fundamental protein of all animal cells." Actually, jake, the most fundamental protein of the Metazoa is collagen. It was the evolution of two uncoded oxygen-dependent amino acids (hydroxyproline and hydroxylysine) that allowed for the evolution of collagens (and extensins in plants). The rapid diversification of the metazoa followed. No collagen; no metazoans. Google: "metazoa connective tissue hydroxyproline" and read about it.

environmental considerations would apply to the genesis of variant/mutants of these. the soup they originate in would be affected by more variable energies/radiations/gammas and solar physics, than what we have in our knowledge base. those parameters are entropic and we have no way to evaluate them or know their part in the cooking up of these basic life structures.

very interesting none the less, but of limited usefulness to solving current social dilemmas. ;-))

But, as much as I enjoy Sci-Fi and armies of clone soldiers in white armor, in reality cloning humans is not needed and it would rise all kinds of moral issues even for non-religious people.

What moral issues?

You clone a human being. You have thus made a new human being. That human being's rights are defined according to the United Nations Declaration of Human Rights as well as your federal, provincial and local laws. Where is the moral issue? Did identical twins suddenly lose rights while I was away? (After all, they are clones of one another!)

We have dealt with the concept of clones for a long time. Our society isn't going to allow raising a clone simply so you can harvest his/her organs. Our society isn't going to allow you to build an army of clones. Our society has already come to terms with the concept that a clone is a human being and as such is entitled to the same rights and freedoms as any other human being.

There will be fringe elements (mostly religious) who try to claim that clones have no rights, because only God can bestow a "soul." (Or some other such nonsense.) But these will be fringe groups. I cannot envision any circumstance (excepting a massive alien invasion that requires us to crank out stupidly high numbers of soldiers ASAP because our population has been devastated) in which we would ever allow clones to be brought into the world without the full suite of rights.

Say what you will about science fiction - or even our politicians - but science fiction has exposed us to the concept for long enough that I think most people would easily agree that a clone deserves full rights.

I mean, hell, engage the man on the street about non-human rights, and most of them will have specific ideas about how smart a computer has to be before it gets rights. I suspect they’d also – on aggregate – agree that non-human sentient/sapient aliens would be deserving of rights. Many even agree that there is a threshold of sapience above which animals should be granted civil rights. (Assuming you can conclusively prove that a non-human animal meets the relevant criteria.)

So I just don’t get the moral issue. Unlike so many other things, this has been hashed out in our literature and fiction already. Before it becomes reality. The internet is a great example. We’ve been exposed to cybernetic dystopias for so long that when people try to clamp down and censor the internet there is a huge backlash. Why? Because our fiction writers have peered down that corridor and shown us what lives there.

Science fiction was a turning point for our species. It was the first time the general populace was exposed to social issues involving futuristic technologies such that they have been forced to think about the potential consequences of major social events before they happen.

I have a generally dim view of humanity on many subjects, but this is one area I just can’t see us screwing up. For all that humans are petty, selfish and self-interested, I refuse to accept that – as a society – we would even pause for a second before declaring that clones are humans and thus get the full suite of rights.

If there is a thorny issue at all in the whole matter it is simply one of guardianship. Who is legally responsible for the clone? A clone is no different from you or I; they will have an 18 year childhood. So who is the legal guardian?

But I suspect that this will depend on “who made the clone.” And can’t be answered with absolute guidance beforehand.

very interesting none the less, but of limited usefulness to solving current social dilemmas. ;-))

Disagree. The more we understand about these primative multicellular organisms, the more we understand about certain subsections of our population. Though, upon reflection, that may be rude to the primative multicellular organisms.

A couple years ago I wouldn't have thought our "society" (in the US) would allow us to detain individuals (including US citizens) indefinitely without anything more than a charge being raised against them. Yet Congress has just specifically allowed that, with the President's signature. If by "society" you mean the mores and cultural standards held by the majority of individuals, you may be right. But these days, it's Congress and the Presidents (i.e., the "political class") that makes the rules, no matter what we have come as a civilization to believe.

A couple years ago I wouldn't have thought our "society" (in the US) would allow us to detain individuals (including US citizens) indefinitely without anything more than a charge being raised against them. Yet Congress has just specifically allowed that, with the President's signature. If by "society" you mean the mores and cultural standards held by the majority of individuals, you may be right. But these days, it's Congress and the Presidents (i.e., the "political class") that makes the rules, no matter what we have come as a civilization to believe.

I'm Canadian. And when I say "our society" I am generally referring to "western society" as a whole. Torturing a handful of people is deplorable, but isn't really the sort of thing that gets governments to bust a move. The violations have to be pretty damned egregious before they'll act. But creating and entire race of slaves? I cannot picture that being allowed.

As a society, we will turn our backs on some pretty bizarre shit. Lots of “-ism” discrimination, wholesale butchering, slaughter in various names, etc. But slavery still gets the blood flowing and a great many people very uppity.

I don’t know about you, sir. But for me, - and for most people I know – that falls into the “worth dying for” category. I can almost accept that other nations periodically get into some jihad situation where tribe A tries to wipe out tribe B. A lot of these countries have some growing up to do.

My country has about 30,000 active servicemen, and only 34 Million people. There is a limit to how much force we can project, and we simply can’t go around playing “clean up after the warlord.”

We can and we do offer peacekeepers for such missions. We can, - and do – economically sanction and political cut off such regimes.

But if a western nation legalised slavery – one of our trusted allies, a nation that had signed multiple treaties upholding human rights in general and banning slavery in particular – I would be on the parliament lawn calling for war.

Even if we lost, that is a fight that must be fought. If for no other reason than to martyr ourselves in front of the international community. To show to rest of the world that there still are nations that care enough to fight the good fight.

The darkest chapters in human history came about because we dehumanised the enemy enough to do things like enslave them, or genocidally attempt to wipe them out. It is bad enough that the odd third-world country hasn’t grown past this. (And I wholeheartedly support Canadian troops on the ground in every possible instance.)

It would be a tragedy beyond comprehension to see a developed nation become corrupted. That is worth my life to prevent; it’s worth the lives of my family.

Some things – some beliefs – you die for. Ensuring slavery stays abolished is one of them.

If enough people feel the same way, then it doesn't matter what the political leadership of one country believes. They will be made to change their minds or there will be hell to pay. If I recall, even in your nation, that is the stuff of civil wars.

Some things – some beliefs – you die for. Ensuring slavery stays abolished is one of them.

Your post is overdone. It doesn't work that way. For example, think of all of the people who think we are already slaves to the banks / international elite / whatever. And yet, because you don't see it, or because various psuedo-slaveries are not race-based, they are ignored.

Evils like slavery don't stay sleeping for long. You may even be among the people who advocates for what someone else considers slavery.

"Some of the holozoans that survive display precisely the mode of reproduction that the authors describe in these fossils",

Those would be the spore states of the Mesomycetozoeans. They are mostly parasitic nowadays and mostly in marine environments (fishes). But they can also be saphrophytic like fungi, which could be the ancestral state in those early ecosystems of the Ediacaran. Here [ http://en.wikipedia.org/wiki/Rhinosporidium_seeberi ] is an infectious and sporal state in humans.

"Ediacaran fossils are clearly multicellular, but lack many of the features shared by all modern animals. In the ensuing period, the Cambrian, all of these organisms are gone, and most of the groups we're familiar with—along with a few unfamiliar ones—are present."

The same Bengtson on that paper is, IIRC, supporting another Ediacaran as the earliest animal, and as a chtenophore lacking some of the modern traits. Another Ediacaran looks rather like an invertebrate or even trilobite relative. So there are at least fossil type of links.

dnjake wrote:

Well a simple general model is that the complexity of eukaryotic cells evolved over a long time until it reached a threshold.

Not really. The class I ribonucleotide reductase (RNR), the enzyme that took the RNA world cells to the DNA world by making DNA out of RNA, unique to eukaryotes is oxygen dependent. While the class III and II of bacteria and archaea is oxygen sensitive respectively insensitive. So eukaryotes evolved after the oxygenation of the atmosphere ~ 2.3 Ga bp.

Multicellularity has been achieved independently ~ 30 times. Even bacteria can be true multicellulars. (Adhering and communicating cells with some specialized for nitrification in cyanobacteria.)

However diversified multicellular ability is confined to ~ 7 times in eukaryotes. And especially from epithelium in slime molds to epithelium and other tissues in metazoa. [ "A Polarized Epithelium Organized by β- and α-Catenin Predates Cadherin and Metazoan Origins", Daniel J. Dickinson et al.] Presumably then catenin, which organizes the gluing together of slime mold cells, is the "most fundamental protein of all animal cells".

The reason for this ability is believed to be the ~ 10^5 times higher energy density that oxygen dependent mitochondria gives to eukaryotes. That energy can be used for protein turnover, utilizing and supporting a larger genome and resulting in an ability to support more traits.

But while mitochondria is universal in eukaryotes it isn't an immediate endosymbiotic acquisition. Megaviruses have been sequenced to phylogenetically derive after the archaea-eukaryote split, they are parasitically simplified . And while these sequences have a large but expanding core of cellular genes the expected mitochondrial genes are lacking. (At least to my layman understanding.)

The putative Mesomycetozoeans here are witnesses of early Ediacaran environment perhaps suitable for saphrophytic life styles and no worry for predation on spore clusters. But like them Megaviruses are witnesses of eukaryotes with endomembrane ability (explaining Megaviral uptake in their hosts but also basic Megaviral capsid capability) but without the energy providers needed for tissues.

As so many times uniformity turns out to be the true rate of change as soon as sampling becomes sufficiently dense.

Some things – some beliefs – you die for. Ensuring slavery stays abolished is one of them.

Your post is overdone. It doesn't work that way. For example, think of all of the people who think we are already slaves to the banks / international elite / whatever. And yet, because you don't see it, or because various psuedo-slaveries are not race-based, they are ignored.

Evils like slavery don't stay sleeping for long. You may even be among the people who advocates for what someone else considers slavery.

If you are honestly attempting to compare the ability to vote in your country's political system, earn a wage, own property, enjoy civil rights etc. (but dear god, you don't wage parity with the guy who spent 10 more years in post secondary than you!) with being the legal property of another human being and enjoying none of the rights and freedoms listed, then we have nothing to talk about.

Slavery is not a joke. It's not something to take lightly, or to invoke because you feel entitled to minor changes in society. There is a great big heaping fuck a difference for "lack of wage equality" and "being owned by another human and having no rights whatsoever."

"Ediacaran fossils are clearly multicellular, but lack many of the features shared by all modern animals. In the ensuing period, the Cambrian, all of these organisms are gone, and most of the groups we're familiar with—along with a few unfamiliar ones—are present."

[quote="dnjake wrote:

Well a simple general model is that the complexity of eukaryotic cells evolved over a long time until it reached a threshold.

The threshold was the evolution of two uncoded, post-translational oxygen-dependent amino acids and their use in the evolution of collagen. If the Ediacaran organisms were not metazoans then they lacked the ability to synthesize collagen. This connective tissue protein is synonymous with Metazoa.